1. Field of the Invention
The present invention is related to an imaging apparatus such as a digital camera. More specifically, the present invention is related to an imaging apparatus and an imaging method that utilizes an imaging element equipped with two types of light receiving elements, which are capable of being controlled and driven independently from each other.
2. Description of the Related Art
CCD's, which are imaging means employed in digital cameras, have narrower dynamic ranges than silver salt film. Therefore, overexposure and underexposure are likely to occur in images photographed by digital cameras. For this reason, various imaging techniques for obtaining image data sets having expanded dynamic ranges have been proposed. A first example of such an imaging technique is that in which a plurality of image data sets which have been obtained under different exposure conditions are combined (refer to U.S. Pat. No. 6,753,920). A second example of such an imaging technique is that in which a CCD, constituted by an arrangement of main pixels (first light receiving elements) having high sensitivities and sub pixels (second light receiving elements) having smaller areas than the main pixels and therefore lower sensitivities but are less likely to be saturated, is utilized. In this technique, high sensitivity image data obtained by the main pixels and low sensitivity image data obtained by the sub pixels are combined, to obtain a combined image data set that exhibits favorable reproduction properties over a wide range from high brightness to low brightness (refer to Japanese Unexamined Patent Publication No. 2008-016862).
Japanese Unexamined Patent Publication No. 2006-148591 discloses an imaging apparatus that employs the aforementioned second imaging technique, in which the driving method of two types of CCD's are switched according to subject field scenes.
Meanwhile, as an example of a technique for imparting different sensitivity differences among light receiving elements, there is a technique in which the exposure times of light receiving elements are set to be different, in addition to varying the areas of the light receiving elements as described above.
In the electronic camera disclosed in U.S. Pat. No. 6,753,920, imaging may be performed with flash. In this case, the flash is excited during a first imaging operation, and the excited state of the flash is maintained for a second imaging operation, to emit flash based on a set exposure ratio while temporarily ceasing flash emission between the first and second imaging operations. Therefore, it is difficult to control flash emission to accurately realize the set exposure ratio. In addition, because two imaging operations are performed, temporal differences occur in the subject within the two obtained image data sets.
Imaging may also be performed with flash in the imaging apparatuses disclosed in Japanese Unexamined Patent Publication Nos. 2008-016862 and 2006-148591. In this case, when imaging operations are performed such that the exposure time of the main pixels are longer than that of the sub pixels and flash is emitted only during the exposure time of the main pixels, the sub pixels perform imaging operations in a state in which no flash is emitted. Therefore, it is difficult to realize set exposure ratios such as 1:2 and 1:4. In addition, if flash is emitted during the exposure times of both the main pixels and the sub pixels, a difference in the amount of emitted light cannot be obtained between the main pixels and the sub pixels. Therefore, it is not possible to realize the set exposure ratio. Further, it is difficult to realize flash emission at a temporal position that results in a set exposure ratio, due to problems of fluctuations in flash emission times.